1. Department of Mathematics, and Institute of Pure and Applied Mathematics, Jeonbuk National University 1 , Jeonju 54896, Republic of Korea
2. Department of Mathematics, Chung-Ang University 2 , Seoul 06974, Republic of Korea
3. Department of Applied Physics, Waseda University 3 , 3-4-1, Okubo, Shinjuku-ku, Tokyo 169-8555, Japan